318 Herr Paul Freund on the Development 



trace of it can be detected. Whether we may assume that in 

 the only slightly younger stages which were investigated by 

 Chabry and Pouchet, a complete dental fold is, as stated by 

 these authors, present throughout the entire diastema of the 

 lower jaw, is a question which I must postpone until 1 have 

 more ample material at my disposal. I do not think it pro- 

 bable that it is so. 



(3) In the upper jaw very extensive remnants of the dental 

 fold are found in the diastema. The fold is not once wanting 

 in any section from the incisor to Stenson's canal : compare 

 figs. 8-10, and the model (fig. 14). In most places the epi- 

 thelial cord is detached from the epithelium of the oral cavity, 

 in others it is connected with it. It frequently appears to lie 

 parallel to the surface of the palate ; the nuclei of the con- 

 nective tissue are disposed in a regular concentric arrange- 

 ment around the epithelial remnant. This is therefore directly 

 contrary to what is stated by Chabry and Pouchet. 



Behind the orifice of Stenson's canals we find for a space 

 no vestige of the epithelial fold : then it is present in certain 

 sections once more, or in its place there appears a kind of 

 cicatrix in the connective tissue. Even before the middle of 

 the space between the orifices of the canals of Stenson and 

 the first molar, we observe a remnant of the epithelial fold as 

 an element which is again regularly visible in every section. 

 At the posterior end it is easy to distinguish the way in which 

 this remnant of the dental fold of the diastema passes into 

 the dental fold of the first molar. It may further be remarked 

 that in this tract also there is much variation ; for the epi- 

 thelial cord may appear larger or smaller, perpendicular or 

 bent round, connected with the epithelium of the oral cavity 

 or isolated. After this discovery it appears scarcely open to 

 doubt, that in younger stages of Sciurus the diastema in the 

 upper jaw is traversed by a continuous dental fold, precisely 

 as in the case of Lepus. 



(4) On the outer side of the dental fold in the diastema 

 there are situated two little enamel-organs with distinct 

 papillae, — one close in front of, and tiie other in the plane of a 

 transverse section through, the orifices of the canals of Stenson 

 {cf. model, fig. 14). These two enamel-organs naturally lie 

 one close behind the other. In both the aperture of the 

 enamel-bell is directed forwards and upwards. The anterior 

 of these two enamel-organs is the better characterized as such, 

 in that it contains enamel-pulp {cf. fig. 7). But that the 

 posterior rudiment is also of the nature of an enamel-germ 

 {cf. fig. 10) is scarcely open to doubt. It is curious that in 

 their fig. 26, MM. Chabry and Pouchet have given a perfectly 



